1. Field of the Invention
This invention relates to an optical modulator adapted to optically modulate a signal by moving electrically charged particles in liquid and also to a method of manufacturing such an optical modulator.
2. Related Background Art
Recently, optical modulators adapted to utilize the electrophoresic phenomenon of electrically charged particles in liquid have been proposed and are expected to find applications in the field of image displays and optical shutters. A known optical modulator for displaying images (to be referred to as electrophoresic display apparatus hereinafter) will be described below as an example of such applications.
In line with the recent technological developments for information devices, there is an increasing demand for energy-saving thin display apparatus. Efforts have been and being paid for research and development in the field of such display apparatus in order to meet the demand. Particularly, liquid crystal display apparatus have been made commercially available as a result of massive development activities. However, currently available liquid crystal display apparatus are still accompanied by certain problems to be solved satisfactorily yet including that the characters on the display screen can be read only with difficulty depending on the viewing angle of the viewer and the amount of light reflected by the screen and that the visual sense of the viewer can be stressed by flickering of the light source and a low luminance level of the displayed image. Under these circumstances, reflection type display apparatus seem to be promising from the viewpoint of low power consumption rate and low stress to the visual sense.
Electrophoresic display apparatus that utilize the electrophoresic phenomenon of electrically charged particles in liquid have been proposed as such display apparatus (see, inter alia, U.S. Pat. No. 3,612,758).
An electrophoresic display apparatus comprises a pair of substrates including an upper substrate and a lower substrate arranged with a predetermined gap interposed between them, insulating liquid filled in the gap between the substrates, a large number of electrically charged electrophoresic particles dispersed in the insulating liquid and display electrodes arranged at respective pixels along the substrates. Partition walls are arranged between adjacently located pixels in order to separate the pixels and prevent the charged electrophoresic particles of a pixel from moving to another so that a uniform concentration of charged electrophoresic particles may be maintained.
Techniques for reliably injecting insulating liquid and charged electrophoresic particles have also been disclosed. Specifically, a technique of arranging holes to be used for injecting liquid to be distributed at positions on the rear surface electrode plate corresponding to the respective holes of a holed spacer and a technique of filling the inside of each pixel with liquid to be distributed by way of a hole arranged on the rear surface electrode plate and sealing the hole by means of a sealing member in the final manufacturing step are known (see, inter alia, Japanese Patent Application Laid-Open No. 1-248183).
A typical conventional method of manufacturing an electrophoresic display apparatus comprises:
forming display electrodes and other related components on a lower substrate;
forming partition walls between adjacent pixels;
an amount of insulating liquid and a substantially equivalent amount of electrically charged particles are filled into each of the recess defined by the partition walls; and
bonding an upper substrate to the partition walls.
When an upper substrate is bonded to the partition walls, insulating liquid is forced out from each recess. At this time, electrically charged particles can also be forced out with insulating liquid. Then, the pixels may not contain a substantially equal amount of charged particles to consequently degrade the quality of the displayed image.
Therefore, the object of the present invention is to provide an optical modulator that can avoid the above identified problem and also a method of manufacturing such an optical modulator.
The present invention is made by taking the above described circumstances into consideration. In an aspect of the present invention, there is provided an optical modulator comprising a first substrate, a second substrate arranged with a predetermined gap interposed between itself and the first substrate, partition wall members partitioning pixels arranged between the substrates, a liquid and a plurality of electrically charged particles arranged at each of the pixels, and first and second electrodes arranged at each of the pixels, the charged particles being adapted to be moved to display an image or operate for optical switching as a result of application of a voltage between the electrodes of each pixel, wherein the first substrate is formed by combining a perforated member having perforations and arranged so as to be held in contact with the partition wall members, the perforations allowing passage of the liquid while obstructing passage of the particles, and a blind member arranged so as to close the perforations.
In another aspect of the invention, there is provided a method of manufacturing an optical modulator comprising a first substrate, a second substrate arranged with a predetermined gap interposed between itself and the first substrate, partition wall members partitioning pixels arranged between the substrates, a liquid and a plurality of charged particles arranged at each of the pixels, and first and second electrodes arranged at each of the pixels, the method comprising a step of forming the partition wall members on the second substrate, a step of placing the liquid and the electrically charged particles in recesses defined by the second substrate and the partition wall members, a step of placing a perforated member on the partition wall members to confine the charged particles in the recesses, and a step of arranging a blind member so as to close the perforations of the perforated member.